CVE-2026-85091: zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate
Noroxi assessment
Priority: Monitor (action score 33/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.46% (FIRST EPSS).
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- Fixed version: azl3 cloud-hypervisor 52.0.152-1 on Azure Linux 3.0 Release Notes; azl3 kata-containers 4.1.0.kata0-1 on Azure Linux 3.0 Release Notes; azl3 zlib 1.3.2-1 on Azure Linux 3.0 1.3.2-2.
Low priority for now. Upgrade to azl3 cloud-hypervisor 52.0.152-1 on Azure Linux 3.0 Release Notes; azl3 kata-containers 4.1.0.kata0-1 on Azure Linux 3.0 Release Notes; azl3 zlib 1.3.2-1 on Azure Linux 3.0 1.3.2-2 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
zlib versions 1.3.1.2 through 1.3.2 contain a heap buffer overflow vulnerability in the gz_vacate() function when processing non-blocking gzwrite() operations with stale external buffer pointers. Attackers can trigger the overflow by calling gzprintf() or gzvprintf() after a write stall, causing an unchecked memmove() to write beyond the internal input buffer boundary.
- Published
- Sep 3, 2026
- Updated
- Sep 9, 2026
- EPSS
- 0.4% · 40th percentile
- CWE
- CWE-787
Report tools
Action score
33
Monitor
Low priority for now.
- CVSS
- 33 / 40 · 8.3 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.4%
CISA SSVC decision
- Exploitation
- proof of concept
- Automatable
- no
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · VulnCheck
- 8.3
- NVD has not scored this yet; the score shown is the CNA’s.
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (VulnCheck). Independent of NVD's CPE analysis and usually ahead of it.
zlib zlib
- 1.3.1.2 and later · up to and including 1.3.2affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Alpine:v3.21 | zlib | before 1.3.2-r1 | 1.3.2-r1 |
| Debian:12 | zlib | from 0 | — |
| openSUSE:Tumbleweed | trivy | before 0.76.0-1.1 | 0.76.0-1.1 |
Same product
zlib: all recordsOther highest-scoring records for the same primary product.
- CVE-2018-25032zlib before 1.2.12 allows memory corruption when deflating (i.e., when compressing) if the input has many distant matches.46Plan
- CVE-2022-37434zlib through 1.2.12 has a heap-based buffer over-read or buffer overflow in inflate in inflate.c via a large gzip header extra field.45Plan
- CVE-2002-0059The decompression algorithm in zlib 1.1.3 and earlier, as used in many different utilities and packages, causes inflateEnd to release certai42Plan
Published before and after this one in the same product
- ← EarlierCVE-2023-45853Oct 14, 2023 · MiniZip in zlib through 1.3 has an integer overflow and resultant heap-based buffer overflow in zipOpenNewFileInZip4_64 via a long filename,40Plan
- ← EarlierCVE-2026-22184Jan 7, 2026 · zlib <= 1.3.1.2 untgz Global Buffer Overflow in TGZfname()18Monitor
- ← EarlierCVE-2026-27171Feb 18, 2026 · zlib before 1.3.2 allows CPU consumption via crc32_combine64 and crc32_combine_gen64 because x2nmodp can do right shifts within a loop that 22Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| azl3 cloud-hypervisor 52.0.152-1 on Azure Linux 3.0 | Release Notes | Microsoft (MSRC) |
| azl3 kata-containers 3.32.0.kata0-2 on Azure Linux 3.0 | — | Microsoft (MSRC) |
| azl3 kata-containers 3.32.0.kata0-5 on Azure Linux 3.0 | — | Microsoft (MSRC) |
| azl3 kata-containers 4.1.0.kata0-1 on Azure Linux 3.0 | Release Notes | Microsoft (MSRC) |
| azl3 zlib 1.3.2-1 on Azure Linux 3.0 | 1.3.2-2 · Release Notes | Microsoft (MSRC) |
| alpine:zlib | 1.3.2-r1 · Alpine:v3.21 | Package registry (OSV) |
| opensuse:trivy | 0.76.0-1.1 · openSUSE:Tumbleweed | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2026-22184239 days apartzlib <= 1.3.1.2 untgz Global Buffer Overflow in TGZfname()18Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- Integrity
- Availability
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- X
Weakness class (CWE)
CWE-787 · Out-of-bounds WriteCVSS vector
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (3 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.